116 lines
4.2 KiB
Haskell
116 lines
4.2 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators
|
|
module Main (main) where
|
|
|
|
import Control.Applicative.Permutations
|
|
import Control.Monad (void, when)
|
|
import Data.Char qualified as C
|
|
import Data.Either
|
|
import Data.Functor
|
|
import Data.List qualified as L
|
|
import Data.Map qualified as M
|
|
import Data.Maybe
|
|
import Data.Set qualified as S
|
|
import Data.Vector qualified as V
|
|
import qualified Data.Vector.Unboxed as VU
|
|
import Data.Void (Void)
|
|
import Text.Megaparsec
|
|
import Text.Megaparsec.Char
|
|
|
|
import Debug.Trace
|
|
|
|
exampleExpectedOutput = 46
|
|
|
|
data Tile = Backslash | Empty | Horizontal | Slash | Vertical deriving Eq
|
|
instance Show Tile where
|
|
show Backslash = "\\"
|
|
show Empty = "."
|
|
show Horizontal = "-"
|
|
show Slash = "/"
|
|
show Vertical = "|"
|
|
type Line = V.Vector Tile
|
|
type Input = V.Vector Line
|
|
|
|
type Parser = Parsec Void String
|
|
|
|
parseTile :: Parser Tile
|
|
parseTile = char '\\' $> Backslash
|
|
<|> char '.' $> Empty
|
|
<|> char '-' $> Horizontal
|
|
<|> char '/' $> Slash
|
|
<|> char '|' $> Vertical
|
|
|
|
parseLine :: Parser Line
|
|
parseLine = do
|
|
line <- some parseTile <* eol
|
|
return $ V.generate (length line) (line !!)
|
|
|
|
parseInput' :: Parser Input
|
|
parseInput' = do
|
|
line <- some parseLine <* eof
|
|
return $ V.generate (length line) (line !!)
|
|
|
|
parseInput :: String -> IO Input
|
|
parseInput filename = do
|
|
input <- readFile filename
|
|
case runParser parseInput' filename input of
|
|
Left bundle -> error $ errorBundlePretty bundle
|
|
Right input' -> return input'
|
|
|
|
type LineOutput = VU.Vector Bool
|
|
type Output = V.Vector LineOutput
|
|
data Heading = N | S | E | W deriving (Eq, Ord, Show)
|
|
data Cursor = Cursor Int Int Heading deriving (Eq, Ord, Show)
|
|
|
|
type Visited = M.Map Cursor ()
|
|
|
|
next :: Cursor -> Cursor
|
|
next (Cursor x y N) = Cursor x (y-1) N
|
|
next (Cursor x y S) = Cursor x (y+1) S
|
|
next (Cursor x y W) = Cursor (x-1) y W
|
|
next (Cursor x y E) = Cursor (x+1) y E
|
|
|
|
compute :: Input -> Int
|
|
compute input = V.foldl' count 0 . fst $ walk startingOutput M.empty startingCursor
|
|
where
|
|
count :: Int -> LineOutput -> Int
|
|
count i l = i + VU.length (VU.filter id l)
|
|
size = V.length input
|
|
startingCursor = Cursor (-1) 0 E
|
|
startingOutput = V.replicate size $ VU.replicate size False
|
|
walk :: Output -> Visited -> Cursor -> (Output, Visited)
|
|
walk output v c | isNothing nextTile = (output, v)
|
|
| justNextTile == Empty = walk output' v c'
|
|
| visited = (output, v)
|
|
| justNextTile == Horizontal = if h == W || h == E then walk output' v c'
|
|
else let (output'', v'') = walk output' v' (Cursor x y E) in walk output'' v'' $ Cursor x y W
|
|
| justNextTile == Vertical = if h == N || h == S then walk output' v c'
|
|
else let (output'', v'') = walk output' v' (Cursor x y N) in walk output'' v'' $ Cursor x y S
|
|
| justNextTile == Backslash = case h of
|
|
N -> walk output' v' $ Cursor x y W
|
|
S -> walk output' v' $ Cursor x y E
|
|
W -> walk output' v' $ Cursor x y N
|
|
E -> walk output' v' $ Cursor x y S
|
|
| justNextTile == Slash = case h of
|
|
N -> walk output' v' $ Cursor x y E
|
|
S -> walk output' v' $ Cursor x y W
|
|
W -> walk output' v' $ Cursor x y S
|
|
E -> walk output' v' $ Cursor x y N
|
|
where
|
|
c'@(Cursor x y h) = next c
|
|
nextTile = case input V.!? y of
|
|
Just l -> l V.!? x
|
|
Nothing -> Nothing
|
|
justNextTile = fromJust nextTile
|
|
line = output V.! y
|
|
visited = M.member c' v
|
|
v' = M.insert c' () v
|
|
output' = if visited then output
|
|
else output V.// [(y, line VU.// [(x, True)])]
|
|
|
|
main :: IO ()
|
|
main = do
|
|
example <- parseInput "example"
|
|
let exampleOutput = compute example
|
|
when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
|
|
input <- parseInput "input"
|
|
print $ compute input
|